1. Field of the Invention
The invention relates to field emission display (FED) devices, and in particular to methods for fabricating field emission display devices.
2. Description of the Related Art
Field emission display (FED) devices are panelized conventional cathode ray tube (CRT) displays. Using screen printing technology, large scale FED devices can be achieved. Conventional larger scale FED devices provide low volume, light weight, low power consumption, excellent image quality, and are applicable to a variety of electronic and communication devices. Carbon nanotube or other nano-scale field emitters have benefits such as low threshold field, high emission current density, and high stability due to lower threshold voltage, higher light efficiency, higher viewing angle, and lower power consumption.
Compared with conventional large scale display devices, CRT displays have excellent display quality but occupy a large amount of space. Projection TVs occupy less space but offer poor display quality. Plasma display panel (PDP) displays exhibit lighter, thinner features and can be fabricated by screen printing, nonetheless, they require high power consumption.
Field emission display (FED) devices are self-emitting display devices including an array of micro vacuum tube field emitters. In operation, electrons are emitted from field emitters by biasing control voltage on the gate electrode while maintaining high voltage on the anode such that the emitted electrons bombard the phosphor with large amounts of energy. The field emitters are conventionally formed by semiconductor thin film process to provide an emitter array on the cathode substrate. The field emitters are typically inorganic materials such as Mo, W, Si, or the like. Field emitters formed by semiconductor thin film process, however, require high cost apparatus and are difficult to achieve on a large scale.
FIG. 1 is a cross section of a conventional field emission display device 10, comprising a lower substrate 11 and an opposing upper substrate 12 with a specific gap G therebetween supported by a wall structure. The lower substrate 11 and upper substrate 12 are sealed in a vacuum. A patterned cathode structure 13 is disposed on the lower substrate 11. A field emitter 14 is disposed on the cathode structure 13. The patterned cathode structure 13 is surrounded by a dielectric layer 15 with a gate electrode 16 thereon.
An anode electrode 17 is disposed on the upper substrate 12. A phosphor layer comprising red 18R, green 18G, and blue 18B elements is disposed on the anode electrode 17. A black matrix (BM) 19 is interposed among the phosphor layer with red 18R, green 18G, and blue 18B elements.
To simplify production processes and achieve large scale display, thick film screen printing is employed to fabricate large scale field emission display devices. Conventional thick film screen printing method, however, forms stacked materials as cathode structure on the lower substrate. The stacks are co-fired or sintered at the same temperature. Some impurity residues may remain on the surface of the electron emission layer, creating porous structure, affecting field emission efficiency.
U.S. Pub. No. 2005/0062195, the entirety of which is hereby incorporated by reference, discloses an adhesive film attached on the field emitters of the lower substrate. The adhesive film is released from the field emitters of the lower substrate, thereby removing impurity residues from the surface and improving electron emission alignment to vertical field.
FIGS. 2A-2B are cross sections of a method for fabricating a FED device using an adhesive film attached on the field emitters of the lower substrate. In FIG. 2A, a substrate 35 with a cathode electrode structure 40 thereon is provided. Patterned isolation structure 50 and gate electrode 60 are formed on the cathode electrode structure 40. A field emission structure 70A is attached on the cathode electrode structure 40 using an adhesive tape 30 as shown in FIG. 2B. The field emission structure 70A, however, exhibits degraded field emission efficiency. Moreover, the adhesive tape 30 cannot be reused, increasing production cost. The surface of the field emitters may be damaged during release of the adhesive tape 30. The organic residue from the adhesive tape 30 may result in the field emitter arching at high operating voltages, degrading properties of the FED devices.
In another conventional method for improving field emission uniformity, the surface of the field emitters is rubbed. The field emitters are well-aligned and provide improved electron emission alignment to vertical field. The roller used in the rubbing, however, may leave residual dust or impurities on the surface of the field emitters, which can result in the field emitter arching at high operation voltage, degrading properties of the FED devices.
Another conventional method for improving field emission uniformity is provided by sandblasting the surface of the field emitters. The field emitters are bombarded by high energy small rigid particles to remove impurities. Some particles may, however, remain, degrading properties of the FED devices.
U.S. Pat. No. 6,890,230, the entirety of which is hereby incorporated by reference, discloses a fabrication method for a field emission display device utilizing laser activation to normalize orientation of carbon nanotubes. FIGS. 3A-3B are a cross section of a conventional method of laser activation to create carbon nanotube (CNT) emitters with uniform orientation. In FIG. 3A, a field emission display device comprises a lower substrate 110 with a cathode 120 thereon. A CNT thick film 130 is formed on the cathode 120 as a field emitter. An upper substrate 160 is disposed opposing the lower substrate 110. An anode 150 is disposed on the upper substrate 160. A voltage controller 140 applies bias between the cathode 120 and the anode 150, thereby controlling the field emission display device. A laser source 170 passing through the upper substrate 160 and anode 150 radiates the CNT thick film 130 to activate the field emitter. FIG. 3B is a cross section of the field emission display device activated by laser treatment of FIG. 3A.
The field emission display device activated by laser treatment can, however, be damaged by undesirable heating. For example, the upper substrate 160, anode 150, dielectric layer and gate electrode may be damaged by laser heating. Moreover, if the laser treatment is performed after the field emission display device is assembled, it is difficult to address and align the laser source, inter alia, for high definition FED devices, resulting in intricate fabrication procedures and reduced throughput.